Method of making aluminum forgings



required times,

chemical atmosphere.

Patented July 3, 1945,

METHOD OF Memo. ALUMINUM roaomos fiKbnneth P. Abbe, Longmeadow,.Mass.

no Drawing.

Application January 2, 1943. Serial No. 471,214

2 Claims. (01,148-214) My invention i an improved method in the art of making'aluminum forgings. It relates particularly to operations of heat treating them. And

my purpose is to substantially avoid the formation of blisters on the forgings during their heat treatment.

I will disclose indetail the way I accomplish this purpose. But the detail involved ca'nbe described more easily against the background of the prior art. So I will refer briefly to the best prior art as now being practicedby some of the -largest plants. Then I will describe in detail the way I have advanced the art. 3

The forgings are now generally treated as'follows in the heat treating operations: They are commonly put in the heat treating furnace, kept under high heat treating temperatures for the taken out and immediately quenched in water, dipped in lye and then in nitric acid solutionsand they. have then been.

heat treated soas to be ready for subsequent operations. This gives the general method. It is well known thatthis treatment commonly'produces blisters giving theproduct -a bad com-v plexion. If the whole surfaceis to be subsequently machined, their'bad complexion presents no problem. It is taken off mechanically and as a mere incident of the machining operations nec.-

essary in any event. But-the forgings'which do not need to he subsequently machined all over their surfaces are commonly objectionable on account of blisters on their unmachinedsurfaces. This is particularly true of forgings made of alu-, minum alloy prepared for high tensile strength. Such forgings are commonly used in airplane construction. .The forgings made of this metal need to be heat treated to give them the desired high tensile strength. The problem presented by the objectionable blisters formed in the heat treatment has been fully recognized; it is a substantial problem; and prior art efforts have been made to meet it.

One suggestion has been to create in the heating furnace a chemical atmosphere having a tendency to avoid or prevent the formation. of blisters on the forgings during the time they are in the furnace. The proposal was to introduce into the furnace a chemical compound in powder form which when subjected to the high temperatures of the furnace melts and gives off the From my personal experience this proposed method does'notwork satisfactorily and there were some indications "that the furnace might beinjured by the special atmosphere so produced. Fabricators customarily find that blisters'form in the heat treating oporation even when this prior art method is used in' an effort to prevent them, and subsequent mechanical operations are necessary even-when a chemical atmosphere such as above described is used.

' I have discovered a method which inpractice,

secures around ninety-nine per cent freedom fromblisters, measured with such care as war'work conditions permit. The indications are that com plete freedom from blisters is obtainable in day to 'day'practice with refinement in technique.

Even under the pressure of war production the use of my method has resulted in only a negli-V gible number of forgings with even a single small blister in them. According to my method I first clean the forgings by dipping them in lye and then in nitric do not believe to be critical. Ten parts by weight of the powder in about one hundred arts by weight of water gives satisfactory results and has been used by me in practice. I first took enough powder to.dissolve in water with the rough idea that its amount should be substantial. That is enough powder was put in the water tobe sure I the liquid compound would not be all water. In

other words a liquid solution'containing more than a trace of borax appears efi'ective in reducing or eliminating the formation of blisters. The borax or sodium borate powder is stirred into the water until all the powder is dissolved.

, The purpose of the initial cleaning step is to prepare the surface of the forgings so that such surfaces will be wet by thesolution and will receive and hold onto a film of the solution.

The forgings, after they have been withdrawn from the solution are fully dried, and the dry forgings are then placed in the furnace and heat treated as desired. When the forgings areremoved from the furnace they are given the usual subsequent dips in water to quench them'and in lye and nitric acid solutions to clean them after? the heat treatment.

The cause of blister formation is an open question-the answer to which is being seriouslysought by experienced and skilled men in the art. They may be caused by one or more factors in the treatment of the product prior to as. well as in the heat treatment. In any event blisters canv I be avoided by using the steps of my method. This pare for the heat treating action in the'fumace, I have avoided blisters on the forgings, which blisters will appear again and in large numbers when my preliminary preparation is not used.

The use of my method not only secures far superior results as compared with other proposed methods but avoids any possible damaging action on the furnace in which the forging are heat treated.

What I claim is:

i. The method which consists in completely and drying the forgings with said solution prior to their said heat treatment step being for the purpose of avoiding blister during said final step.

2. The method which consists in the following 5 steps: cleaning forgings of aluminum which need to be heat treated at high temperatures below the fusion point, the cleaning of the 'iorgings being done for the purpose of preparing all their surfaces for wetting prior to the heat treatment,

10 wetting the cleaned surfaces with a liquid solu- KENNETH P. ABBE.

15 Purp se described. 

